The odontoblast is a unique cell type which is responsible for the elaboration of the organic matrix of dentin. Initially pivotal in tooth morphogenesis, it becomes equally as integral in the protection and maintenance of the fully formed tooth, Traditionally this cell has not been amenable to simplistic experimental models due to its highly differentiated and post-mitotic state. Partial characterization of the odontoblast has been accomplished using biochemical, microscopic and, most recently, molecular techniques, predominantly in rodent systems. A full characterization of the human odontoblast, however, is lacking., The overall aim of this proposal is to develop a model whereby odontoblast- specific transcripts may be identified for both quiescent and stimulated odontoblasts. We propose to do this by performing subtractive hybridization between human odontoblast mRNA and that of primary human osteoblasts. Unique transcripts will be identified by dot blot hybridization and Northern blot analysis and characterized by sequence analysis. Unique transcripts can then be used as probes in situ hybridization to verify their scope of expression in a variety of tissues. Confirmed odontoblast specific transcripts will be used as probes to screen human genomic libraries for the complete gene sequence of selected clones to study gene processing and regulation and thereby describe the role of genetic regulation in reparative dentinogenesis. Future studies would include the utilization of odontoblast-specific transcripts as differentiation markers for identifying progenitor cell pools as well as application of the proposed technique to study different activation states of human odontoblasts